In a manufacturing process of a semiconductor element that requires a crystal film relatively large in the film thickness as in a power device such as an IGBT (Insulated Gate Bipolar Transistor), an epitaxial growth technique that enables to form a film by vapor-phase growing a single-crystal thin film on a substrate such as a wafer is conventionally used.
In a film forming apparatus used in the epitaxial growth technique, for example, a wafer is placed inside of a film forming chamber kept at an ordinary pressure or a reduced pressure. While the wafer is heated, gases serving as materials for film formation (hereinafter, also simply “material gases”) are supplied into the film forming chamber. A pyrolysis reaction and a hydrogen reduction reaction of the material gases then occur on a surface of the wafer and an epitaxial film is formed on the wafer.
To manufacture an epitaxial wafer large in the film thickness at high yield, it is necessary to successively bring fresh material gases into contact with the surface of the wafer uniformly heated to increase the rate of vapor-phase growth. For this purpose, the epitaxial growth is performed while the wafer is rotated.
In a conventional SIC epitaxial apparatus, an SIC film is deposited not only on a wafer but also on a surface of a susceptor that holds the wafer. A structure in which a cover is mounted on the susceptor to protect the susceptor is therefore used.
When SIC is used for the susceptor, under a high temperature equal to or higher than 1400° C., there is such a problem that SiC of the susceptor sublimates due to a temperature difference from the wafer at a position where the wafer is placed on the susceptor and adheres to the bottom surface of the wafer. When a material other than SIC is then used for the susceptor, SIC deposited on the susceptor easily peels off and becomes a particle source.
When a cover of an SiC material is provided on the susceptor as mentioned above to solve this problem, SIC of the cover then sublimates and adversely adheres to the susceptor this time. An object of the present invention is to provide a film forming apparatus, a susceptor unit, and a film forming method that can suppress adherence of SIC to a susceptor.